A multi-carrier communication system such as, e.g., Orthogonal Frequency Division Multiplexing (OFDM), Discrete Multi-tone (DMT) and the like, is typically characterized by a frequency band associated with a communication channel being divided into a number of smaller sub-bands (subcarriers herein). Communication of information (e.g., data, audio, video, etc.) between stations in such a multi-carrier communication system is performed by dividing the informational content into multiple pieces (e.g., symbols), and then transmitting a number of pieces in parallel via the separate subcarriers. When the symbol period transmitted through a is subcarrier is longer than a maximum multipath delay in the channel, the effect of intersymbol interference between the subcarriers may be significantly reduced.
A limitation in any wireless communication system is the impairment of the channel as a result of fading, noise and the like, and multi-carrier communication channels are similarly susceptible to such problems. FIG. 1, for example, graphically depicts a multi-carrier communication channel 102, wherein a number of the total distribution of subcarriers 104 are adversely attenuated as a result of noise 106. One approach to try and mitigate the effect of random channel conditions such as noise and fading is to employ interleaving techniques.
Conceptually, an interleaver in a transmitter rearranges input data to spread-out contiguous data of an input data stream across multiple disparate blocks of data in an output data stream. Reversing this process, a de-interleaver in a receiver will rearrange the interleaved data back to the original sequence. In this regard, interleaving introduces a form of temporal diversity, separating information that was adjacent to one another in the original data stream across a number of blocks in the interleaved data stream. In so doing, bursts of errors that might otherwise result in lost packets at the receiver appear to the receiver as independent channel error, which may be readily handled through other error correction techniques.
Conventional interleaving techniques, however, may be insufficient at curbing the problems illustrated in FIG. 1. In a conventional IEEE 802.11a wireless communication system, for example, interleaving is performed by receiving content sequentially in a row-wise fashion into rows, and then iteratively reading out the content in a sequential, column-wise fashion (i.e., a read interval of one (1)). This interleaving technique results a subcarrier separation (or, span) of three (3) subcarriers between adjacent bits of the input signal. Given a subcarrier size of 312.5 KHz (in our 802.11a example), an instance of a noise signal that has a bandwidth of 937.5 KHz or greater (e.g., a 1 MHz Bluetooth signal within the same band) may adversely affect three (3) adjacent subcarriers, resulting in packet loss in the 802.11a receiver.
Thus, an improved interleaver architecture and related methods are required.